In traditional circuit-switched telephony systems, emergency services are available for subscribers in situations of emergency, such as accidents and diseases. Emergency calls are typically first routed to an emergency centre which then connects the calls further to relevant emergency service stations, depending on the current situation, e.g. a hospital, a fire station or the police.
Details and requirements of emergency services are subject to regulations prevailing in different countries and regions. Typically, it is required that the telephony system can provide relevant location information in order to certify the location of the calling party. Firstly, it may be important to connect an incoming call to an emergency centre or service station being reasonably close to the caller. Secondly, the caller may not for some reason be able to provide crucial information regarding his/her whereabouts during the call to the emergency centre, at least not immediately.
In fixed public networks such as a PSTN (Public Switched Telephony Network), it is typically required that local exchanges therein add a “calling party identifier” to emergency calls when routed to an emergency centre. A local exchange has knowledge of which subscribers are connected to specific input lines in the exchange, each being associated with a specific calling party identifier, and adds such a calling party identifier to emergency calls. The emergency centre can then retrieve the geographic location from a location database in the public network by means of the received calling party identifier.
However, the location of a subscriber terminal is not permanent in the same way as before, and a terminal can be connected to an access network more or less regardless of its current geographic location, while still using the same subscriber identity. This is evidently the case for mobile terminals, but also for fixed portable terminals that can be jacked into different access points at different locations e.g. in an IP access network, e.g. for accessing various “broadband” services.
FIG. 1 is a simplified illustration of a mobile subscriber terminal A connected to a circuit-switched cellular mobile access network 100 by means of radio connection with a base station 102 providing radio coverage in a cell where the subscriber is currently located. An emergency centre 104 can be reached by subscribers in the network 100 over a transit network (not shown) such as PSTN/ISDN (Integrated Services Digital Network). In the figure, subscriber A makes an emergency call by dialling an SOS number or the like. The base station 102 is connected to an MSC (Mobile Switching Centre) 106 in the network 100, which routes the call to the emergency centre 104.
Network 100 further comprises a mobile positioning centre 108 adapted to provide location information on mobile subscribers in the network 100, including subscriber A, e.g. as geographic coordinates or the like. The position of subscriber A may be determined based on the identity of the cell in which the emergency call is made, which can be obtained from the serving MSC handling the call. This information could be sufficiently accurate, e.g. if the subscriber is located in a relatively small cell. However, more precise location information may also be obtained by means of a positioning function using various advanced methods. For example, the position of a connected mobile terminal can be calculated from signal strength measurements in the base station 102 and/or neighbouring base stations, sometimes referred to as “triangulation”. Further, some mobile terminals are equipped with a GPS (Global Positioning Satellites) unit interacting with a GPS system, such that the positioning function can receive GPS based location information from either the terminal or from the GPS system.
Thus, the serving MSC 106 can supply location information to the emergency centre 104 when routing the call thereto, such as a cell identity or more specific information. The emergency centre 104 may also use available location services employed in the network 100, to determine the location of the calling party, if necessary.
In order to support emergency services, two main information elements have been defined in the current call control signalling standards ISUP (ISDN User Part) and BICC (Bearer Independent Call Control) for circuit-switched networks, namely “calling geodetic location” and “location number”, the former indicating the geographic position of a calling party and the latter identifying a geographical area such as a region, country, city, etc. BICC is a call control protocol used between serving nodes. This protocol is based on the ISUP protocol, and was adapted to support the ISDN services independent of the bearer technology and signalling message transport technology used.
Further, the standard J-STD036-A defines an architecture connecting a circuit-switched mobile network with an emergency services network and messages required to identify and locate a calling party. Among other things, in support of location determination of subscribers making emergency calls, J-STD036-A defines functionality referred to as “MPC (Mobile Positioning Centre)” and “GMLC (Gateway Mobile Location Centre)” in mobile access networks, and “CRDB (Coordinate Routing Database)” in emergency services networks. For example, in a circuit-switched mobile network using the ANSI-41 standard, the node MPC communicates with MSC nodes over interface E3, with the CRDB node in an emergency services network over interface E11, and with an emergency services network over interface E2. In a circuit-switched mobile network using the PCS 1900 standard, the node GMLC communicates with MSC nodes over interface Lg, with the CRDB node in an emergency services network over interface E11, and with an emergency services network over interface E2.
Although the examples above are relevant for traditional circuit-switched telephone networks, the evolution of telecommunication is generally moving towards packet-switched networks. Various communication networks and terminals are used today that are capable of packet-based multimedia communication using IP (Internet Protocol), including fixed or mobile computers and telephones. Multimedia services typically entail IP based transmission of encoded data representing media in different formats and combinations, including audio, video, images, text, documents, animations, etc.
It has not yet been solved how to provide the necessary location information in support of emergency calls over packet-switched IP networks. It is possible to employ an architecture connecting a packet-switched mobile network with an emergency service network and signalling messages according to the standard J-STD036-A, but this would result in great costs and delays. An alternative and simpler inter-working solution is desirable in this context.
A network architecture called “IP Multimedia Subsystem” (IMS) has been developed by the 3rd Generation Partnership Project (3GPP) as an open standard for handling multimedia services and communication sessions in the packet domain. IMS networks can also be used for emergency services, although it remains to be solved how to provide relevant location information when required. IMS is a platform for enabling services based on IP transport more or less independent of the access technology used, and will be briefly outlined here.
The IMS network is thus used for generally controlling multimedia sessions, and a specification called “SIP” (Session Initiation Protocol, according to the standard IETF RFC 3261) is used for handling multimedia sessions in IMS networks. SIP is an application-layer protocol used by IMS networks and terminals to establish and control IP based multimedia communications. When sending SIP messages, an addressing element called “SIP URI” (Uniform Resource Identifier) is used, such that one SIP URI indicates the source and another one indicates the destination in each message.
FIG. 2 is an exemplary schematic illustration of a basic scenario when multimedia services are provided for a mobile terminal A by means of an IMS service network. Terminal A is connected to a mobile access network 200 and communicates media with a remote party B, such as another terminal or server, in an IP communication session S. An IMS network 202A is connected to the mobile access network 200 and handles the session with respect to terminal A, where networks 200 and 202 are typically owned by the same operator. Moreover, if a terminal is connected to a visited access network, multimedia services are handled by the terminal's “home” IMS network, i.e. where it is registered as a subscriber. The remote party B may be connected to another corresponding IMS network 202B. It should be noted that mobile access networks of today are typically divided into a circuit-switched domain and a packet-switched domain.
The illustrated session S is basically managed by a node called S-CSCF (Serving Call Session Control Function) 204 assigned to terminal A in the IMS network 202A, and the used multimedia service is enabled and executed by an application server 206 connected to the IMS network 202. Basically, the S-CSCF node 204 serves as a proxy for the application server 206 towards terminal A, and sends SIP messages coming from terminal A towards the remote party B, as indicated by a dashed arrow. Further, a main database element HSS (Home Subscriber Server) 208 stores subscriber and authentication data as well as service information, among other things, that the application server 206 can fetch for executing services for subscribers.
A node called I-CSCF (Interrogating Call Session Control Function) 210 in IMS network 202 is connected to other IMS networks, including network 202B, and acts as a gateway for SIP messages arriving from such IMS networks. I-CSCF 210 receives SIP messages concerning the remote party B, as indicated by another dashed arrow. Another node in IMS network 202 called P-CSCF (Proxy Call Session Control Function) 212 acts as an entry point towards the IMS network 204 from any access network, such as mobile network 200, and all signalling messages between subscribers of the IMS network 204 are routed through the P-CSCF 212.
Of course, the IMS network 202 contains numerous other nodes and functions, such as further S-CSCF nodes and application servers, which are not shown here for the sake of simplicity. For example, media gateways (MGW) are used for generally converting packet-switched transport into circuit-switched transport, and a node called “Media Gateway Control Function” (MGCF) translates packet-switched IMS signalling (e.g. according to SIP) into circuit-switched signalling (e.g. according to ISUP).
As indicated above, it is desirable to satisfy prevailing emergency requirements for providing location information to an emergency centre for mobile subscribers in a safe and reliable manner, when emergency requests are made over an IP based multimedia service network, such as an IMS network using SIP signalling. However, it is a problem that signalling protocols for emergency networks have typically been implemented in the circuit-switched domain e.g. using ISUP signalling. To implement emergency services wholly in the packet domain, e.g. according to the standard J-STD036-A described above, would result in great costs and deployment delays.
In 3GPP, it has been proposed that a mobile terminal making an IP session request for an emergency call in a packet-switched mobile access network, e.g. by means of an SIP INVITE message, should supply the cell identity along with the request to the network. Thereby, the access network can select the most appropriate emergency centre based on the supplied cell identity, potentially using other network based location services as well, and route the request thereto. However, it has not been solved how to provide the location information to an emergency centre in the circuit-switched domain.
It is thus desirable to support emergency calls with location information when IP based multimedia services and networks are used. It is also desirable to maintain existing circuit-switched standards and infrastructures in emergency networks when providing such location information in emergency sessions by means of an IP based multimedia service network.